How to determine redline?`
Thread Starter
Pro
Joined: Apr 2001
Posts: 545
Likes: 0
From: Waukesha WI
How to determine redline?`
I know this will probably spark much debate, but what is the generally accepted way to determine what you redline is. My origional motor was an L48 with a 5500 rpm redline. I have gone to a non stock block (an inexpensive short block), and top end parts listed in my profile. For all practical purposes, I chose parts (heads, cam) that desktop dynoed at a max of maybe 5000 or 5500 to push it. They fall off power and tq wise after 6k. I dont really wish to push it ever more than that, but wondering what are the determining factors.
Safety Car
Joined: Aug 2000
Posts: 3,909
Likes: 26
From: Clymer PA
Re: How to determine redline?` (DollaGreen)
One of the biggest determining factors of how high you can rev your engine is your rod/stroke ratio. The lower the rod/stroke ratio number, the higher the piston speed at any given RPM. To determine the rod/stroke ratio, divide your rod length by your stroke. I.E. a 454 big block 6.135" rod / 4.00" stroke = 1.53 rod stroke ratio.
Obviously forged rotating assembly componants (specifically rods and pistons) will gain you a few extra RPMs of revving capability. You really need to find out where your setup makes the most power. If it's not going to make power past 6000RPMs there's not much sense in revving it any further. Revving a motor to 6000RPMs is not that hard on it. I know the factory redline is 5500RPMs but if your setup will make power up to 6000RPMs I see no harm in revving it that high. A stock L48 motor with decent mileage can easily handle 6000RPMs.
Obviously forged rotating assembly componants (specifically rods and pistons) will gain you a few extra RPMs of revving capability. You really need to find out where your setup makes the most power. If it's not going to make power past 6000RPMs there's not much sense in revving it any further. Revving a motor to 6000RPMs is not that hard on it. I know the factory redline is 5500RPMs but if your setup will make power up to 6000RPMs I see no harm in revving it that high. A stock L48 motor with decent mileage can easily handle 6000RPMs.
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Re: How to determine redline?` (DollaGreen)
For racing purposes I've heard that you should shift a little past your powerpeak RPM to stay in the fat part of the powerband when you shift. Approx. 300-500 RPMs past peak power is probably a safe bet but your cam manufacturer should be your best source for redline- they know what their cam/lifter/spring combo can pull safely.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: How to determine redline?` (DollaGreen)
My understanding of "redline" rpm is the rpm where the engine no longer gains HP which doesn't mean that the engine would get damaged if reving higher... For racing it's recommended to shift 200 RPM past peak HP...
:cheers:
Olivier
:cheers:
Olivier
Safety Car
Joined: Apr 2001
Posts: 4,795
Likes: 1
From: Regina Saskatchewan, Canada.
Re: How to determine redline?` (GrandSportC3)
My old setup used to make power to just over 6000rpm and the good shifts were at 6700. Those extra few rpms sure do make a difference.
Melting Slicks
Joined: Dec 2000
Posts: 2,635
Likes: 0
From: Union Ontario
Re: How to determine redline?` (Stingy74)
While engine components do help determine a redline to some extent, the camshaft is what determines it mostly. The camshaft can be thought of as the brain to your engine...... it tells your engine what to do and when to do it. If you have a stock L-48 cam, the engine can spin up to 6500RPM probably but you are out of your powerband by 5500.
Prime example for me is my 278 energizer is redlines at 6500RPM. So at the drag strip I shifted at 6500RPM. when I started shifting at 5500-5750RPM, I gained 1/2 sec in the quarter mile. my redline of the cam may be 6500 but my power peak is around 5250-5700rpm. So for all intents and purposes, the redline of my car should be 5750.
The only time parts will determine the redline is when you start spinning the engine up higher(6500 and up) and if you are going to spin your engine that fast chances are you'll have good forged parts in there already.
Prime example for me is my 278 energizer is redlines at 6500RPM. So at the drag strip I shifted at 6500RPM. when I started shifting at 5500-5750RPM, I gained 1/2 sec in the quarter mile. my redline of the cam may be 6500 but my power peak is around 5250-5700rpm. So for all intents and purposes, the redline of my car should be 5750.
The only time parts will determine the redline is when you start spinning the engine up higher(6500 and up) and if you are going to spin your engine that fast chances are you'll have good forged parts in there already.
Advanced
Joined: Apr 2002
Posts: 80
Likes: 0
From: SOMERSET NJ
Re: How to determine redline?` (GrandSportC3)
If you had no tach how would you Know when to shift .With a shift light ?
If you had no shift light?How about seat of the pants? Can you feel the car nose over?When you drive your car hard can you feel when it stop pulling thats when you shift. Any thing past that is red line.But this is OLD SCHOOL
:cheers: I wish my stock camed L48 pulled TO 5500 then I would not have To shift at 4000/4200
Walt
[Modified by MY63Z11, 8:42 PM 9/2/2002]
If you had no shift light?How about seat of the pants? Can you feel the car nose over?When you drive your car hard can you feel when it stop pulling thats when you shift. Any thing past that is red line.But this is OLD SCHOOL
:cheers: I wish my stock camed L48 pulled TO 5500 then I would not have To shift at 4000/4200
Walt
[Modified by MY63Z11, 8:42 PM 9/2/2002]
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Oct 1999
Posts: 2,581
Likes: 14
From: Tolar Texas
Re: How to determine redline?` (DollaGreen)
All of these answers sound valid to me.
In summary, my simplified view on this subject is that redline is the maximum rpm that any particular engine combination can spin before mechanical damage occurs OR to the point where power stops increasing. Whichever is less would be the "red line".
In summary, my simplified view on this subject is that redline is the maximum rpm that any particular engine combination can spin before mechanical damage occurs OR to the point where power stops increasing. Whichever is less would be the "red line".
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
Re: How to determine redline?` (MIKER)
Red line is where its dangerous to get mechanical damage. As for what are the limiters...the first one u'll encounter is the cam. If its hydraulic, it'll float at around 6500...maybe 7000 with high perf lifters. Next problem is the crank...the more your rod/bore ratio is the more stress ur putting on the crank thus requiring a stronger one. So its common to reduce the ratio to remove some stress on the crank. Another point is valve lift...the more u have the bigger springs u want...but more springs normally means a shorter lifter/cam life. All an all...a stock setup can handle 6500. a fullproof racing engine can see 10,000. Its really hard to tell what will be the redline for an engine.
Safety Car
Joined: Feb 1999
Posts: 3,631
Likes: 14
From: Fountain Hills AZ
Re: How to determine redline?` (MIKER)
The limiting factor is usually the valvetrain, not just the cam but the lifters, springs, etc.. In some cases, where the valvetrain is optimum and valve control is no longer an issue, the bottom end, especially the ability to provide adequate oiling, can become a major limitation. Except for a few cases, piston speed is not much of an issue in determining an engine's redline.
As others have posted, revving an engine beyond it's peak power will usually benefit acceleration. Though the accelleration rate will drop off once past peak hp, "over revving" will result in starting the next gear at a higher a higher rpm and therefore with more power. An example of this was a car I used to run at the drags. It's power peaked at 5,800 rpm. With it's stock 3.55 gears (which were later changed to 4.10's and 4th gear became more usable) I was running 13.9 @ 109mph if I shifted to 4th but by winding it out and crossing thr traps in 3rd at 6,600 rpm, I would run 13.7 but at 105mph. I did break a valve spring using that tactic (covered under warranty :)). After a cam/lifter/spring replacement with Isky parts, my new redline became 6,800 rpm though it's power peak was now closer to 6,200 rpm and I was running well into the 12's.
As others have posted, revving an engine beyond it's peak power will usually benefit acceleration. Though the accelleration rate will drop off once past peak hp, "over revving" will result in starting the next gear at a higher a higher rpm and therefore with more power. An example of this was a car I used to run at the drags. It's power peaked at 5,800 rpm. With it's stock 3.55 gears (which were later changed to 4.10's and 4th gear became more usable) I was running 13.9 @ 109mph if I shifted to 4th but by winding it out and crossing thr traps in 3rd at 6,600 rpm, I would run 13.7 but at 105mph. I did break a valve spring using that tactic (covered under warranty :)). After a cam/lifter/spring replacement with Isky parts, my new redline became 6,800 rpm though it's power peak was now closer to 6,200 rpm and I was running well into the 12's.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Re: How to determine redline?` (Vetterodder)
Another factor is if your motor was balanced properly when it was built, you can put a 4000-7500 RPM cam in there but if it blows up at 6000 then I would say 5500 RPM was the redline for that particular motor :D
Race Director
Joined: Oct 2000
Posts: 15,044
Likes: 79
From: central FL, near the beach.
Re: How to determine redline?`
with H lifters 5800-6000 according to a recent magazine test.
this is the H lifter redline.
While it is possible to push H lifters higher, go with a solids if you need more rpm.
this is the H lifter redline.
While it is possible to push H lifters higher, go with a solids if you need more rpm.
Team Owner
Joined: Jul 2001
Posts: 182,997
Likes: 88
From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Re: How to determine redline?` (Matt Gruber)
..., go with a solids if you need more rpm.
:cheers:
Olivier
Team Owner
Joined: Aug 1999
Posts: 42,487
Likes: 47
SPARTAN
CI 3-4-5-6-8-9-10 Vet
CI-9 AutoX Winner
CI-3 Go Kart Champ
St. Jude '03-'04-'05-'06-'07-'08-'09-'10-'11
Re: How to determine redline?` (Matt Gruber)
with H lifters 5800-6000 according to a recent magazine test.
this is the H lifter redline.
While it is possible to push H lifters higher, go with a solids if you need more rpm.
this is the H lifter redline.
While it is possible to push H lifters higher, go with a solids if you need more rpm.
Redline, as I understand it, is a matter of where valve float occurrs and a matter of piston velocities and accelerations combined with the strength of the recirculating assembly (crank & rods). But in all my engine-related engineering books, I have yet to find any specific mention of how to calculate it.
Race Director
Joined: Oct 2000
Posts: 15,044
Likes: 79
From: central FL, near the beach.
Re: How to determine redline?` (ddecart)
red is danger. redline is danger zone.
What is dangerous is an opinion. i had my H 61 to 7000 at least twice. my opinion is it was in the danger zone.
Consider how opinions vary as to maximum temp. in traffic. 230 is ok by me, but many people panic because their opinion is different, or because their car actually boils over by then.
When redline is exceeded it doesn't necessarily blow up, it might be damaged, but we hope not.
What is dangerous is an opinion. i had my H 61 to 7000 at least twice. my opinion is it was in the danger zone.
Consider how opinions vary as to maximum temp. in traffic. 230 is ok by me, but many people panic because their opinion is different, or because their car actually boils over by then.
When redline is exceeded it doesn't necessarily blow up, it might be damaged, but we hope not.
Drifting
Joined: Jun 2001
Posts: 1,809
Likes: 0
Re: How to determine redline?` (DollaGreen)
I learned a lot on this thread, one thing that was left out was fuel starvation. This depends on the fuel setup (intake, carb, clean filter) if your engines starts sounding different like it's dropping off it time to shift.
Drifting
Joined: May 2001
Posts: 1,651
Likes: 13
From: Holly MI
Re: How to determine redline?` (DollaGreen)
Redline is normally based on the RPM where your valvetrain can no longer guarantee that all the parts stay in contact. In other words, how many RPM's before you float valves or toss pushrods. The valvetrain is the limiting factor in almost every case. The way to increase redline is to remove friction and/or mass from your valvetrain. Friction and mass increase the force required to accelerate the parts. These are the things we calculate at work every day. To really calculate your redline, you need the exact geometry of your engine, the part masses, centers of gravity, and coefficients of friction. Also, keep in mind that OEM's will always add a safety factor to the redline to keep people like us from blowing engines up. :D
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: How to determine redline?` (bb69)
You have to build two identicle motors. Then fire one up on a test stand which loads the motor. Slowly increase the rpm untill it blows up. Then place your redline 500 rpm lower than the blowup number on the second one and install it in your car. :cheers:
